Field of the Invention
The invention relates to a radio-frequency coil assembly for magnetic resonance imaging, as well as to a method for determining a position of a housing element of a radio-frequency coil assembly, and to a magnetic resonance apparatus having such a radio-frequency coil.
Description of the Prior Art
In a magnetic resonance apparatus, also known as a magnetic resonance tomography system, the body of an examination subject, such as a patient, that is to be examined is exposed by operation of a basic field magnet, to a relatively high basic magnetic field of, for example 1.5, 3, or 7 Tesla. In addition, gradient fields are applied with the use of a gradient coil assembly. Radio-frequency pulses, for example excitation pulses, are then transmitted via an excitation system by appropriate antenna devices, which result in the nuclear spins of certain atoms that have been resonantly excited by these radio-frequency pulses to be tilted by a defined flip angle with respect to the magnetic field lines of the basic magnetic field. During the relaxation of the nuclear spins, radio-frequency signals, known as magnetic resonance signals, which are received by an appropriate radio-frequency coil assembly and then further processed, are emitted. To receive the magnetic resonance signals, the radio-frequency coil assembly can include at least one radio-frequency antenna. The desired image data can be reconstructed from the raw data acquired in this way.
Such a radio-frequency coil assembly for receiving the magnetic resonance signals can be designed as a local radio-frequency coil assembly. Such a local radio-frequency coil assembly is usually positioned in a patient accommodation region of the magnetic resonance scanner in direct proximity of the patient to receive the magnetic resonance signals. This means that the local radio-frequency coil assembly can detect the magnetic resonance signals in the proximity of their place of origin in a particularly advantageous manner. The local radio-frequency coil assembly can be arranged at various positions on the patient and is frequently designed in a flexible manner. A local radio-frequency coil assembly therefore often has an unknown geometry and/or an unknown arrangement and/or an unknown position during the scan.
In certain applications it is desirable to determine the spatial position and/or geometry of the local radio-frequency coil assembly during a magnetic resonance scan. This is an advantage in particular when the local radio-frequency coil assembly is used to acquire magnetic resonance signals for magnetic resonance scans in combination with a positron emission tomography scan (PET scan). The combination of magnetic resonance scans with PET scans requires knowledge that is as precise as possible with regard to the position and/or the arrangement and/or the geometry of the local radio-frequency coil assembly in order to determine with precision any signal attenuation that photons in a PET scan experience when passing through the local radio-frequency coil assembly. If the local radio-frequency coil assembly is not taken into account in the attenuation correction, this can lead to PET events being missed in the PET data and/or to image artifacts in the reconstructed image data.